The present invention relates to the field of sulphurized olefins and its subject is more particularly a novel process for preparing pale-coloured sulphurized olefins, by sulphurization using sulphur and hydrogen sulphide.
Sulphurized olefins are products widely used for sulphurizing catalysts, and as additives for lubricants or for elastomers. These products are essentially composed of mixtures of organic sulphides, disulphides and polysulphides.
The person skilled in the art knows of numerous processes for preparing sulphurized olefins or organic polysulphides. A first family of processes reacts a mercaptan and sulphur in the presence of a basic catalyst. These processes, described in the patents FR 2 607 496 and FR 2 630 104, for example, are costly since they require the use of mercaptans, which themselves have to be produced from olefins or alcohols.
The process described in the patent EP 342 454 for preparing dialkyl disulphides and dialkyl polysulphides from olefins is in fact a two-step process, where an H2S+olefin reaction is first carried out in the presence of a solid catalyst to form a mercaptan and, secondly, this mercaptan is brought into contact with sulphur and with another heterogeneous catalyst to form a polysulphide. This process has the disadvantage of requiring two steps in succession (2 different reactors) with elevated temperatures.
Other processes which can give sulphurized olefins have been proposed:
1) The olefin+sulphur reaction in the absence of H2S generally produces coloured products. To avoid this disadvantage it has been proposed to work the process in the presence of water or to carry out water washing, but this creates problems in the separation of the aqueous phase and the disposal of aqueous effluents. Processes of this type are described in the patents U.S. Pat. No. 5,338,468, WO 92/03524, WO 92/00367, WO 97/24416, EP 714 970, EP 714 971 and FR 2 757 534. In all these processes, elevated temperatures are required for good conduct of the reaction. The patent EP 201 197 describes the sulphur+olefin reaction at a temperature of from 140 to 180xc2x0 C.
2) The olefin+sulphur+H2S reaction has been described. The absence of catalyst, as in the patent U.S. Pat. No. 4,119,550, forces the use of very high temperatures and pressures. The patents EP 889 030, U.S. Pat. No. 4,119,549, U.S. Pat. No. 4,191,659, U.S. Pat. No. 4,584,113 and JP 11-246518 describe this reaction with a homogeneous catalyst, which is difficult to remove at the end of the reaction. The patent EP 554 011 describes this same reaction in the presence particularly of heterogeneous catalysts which have moderate efficacy in terms of conversion at 110xc2x0 C.
A novel process has now been found for preparing sulphurized olefins by sulphurization using sulphur and H2S, giving clear, pale-coloured products and allowing the reaction to be realized in a single step.
The process according to the invention is characterized in that the reaction is carried out in a single step in the presence of a zeolite with a medium or large pore size (from 0.5 to 0.8 nm).
The zeolite to be used according to the invention is an aluminosilicate characterized by a large specific surface area and a specific pore size. The general chemical formula is M2/nO.Al2O3.ySiO2.wH2O, where M is the cation, n is its valency, w is the amount of water of crystallization and y is greater than or equal to 2. The zeolite may be exchanged with alkali metal cations, such as Na+, Li+, K+ or Cs+, or alkaline earth metal cations, such as Mg2+ or Ca2+, or metal cations, such as Ag+, Co2+, Ni2+, Mo2+ or 3+, Fe2+ or 3+, Cr3+, La3+ etc. It may also be exchanged with ammonium ions or with the H+ ion.
Although many factors can affect the catalytic activity of these zeolites, the three most important are: the structure of the skeleton and its pore size, the silica/alumina ratio in the skeleton and the nature of the cations. The zeolites according to the invention are zeolites with a medium or large pore size, in the range from 0.5 to 0.8 nm. These zeolites are preferably of type X, Y, L or mordenite, and more preferably of type Y. These zeolites are described in the Handbook of Molecular Sieves, R. Szostak, Van Nostrand and Reinhold, New York 1992. For example, the type X fundamental unit in the hydrated state typically has a chemical composition of Na86.[AlO2)86.(SiO2)106].264 H2O with pores of diameter 0.74 nm; the type Y fundamental unit in the hydrated state typically has a chemical composition of Na56.[(AlO2)56.(SiO2)136].264H2O with pores of diameter 0.74 nm; the type L fundamental unit in the hydrated state typically has a chemical composition of K9.[(AlO2)9.(SiO2)27].22H2O with pores of diameter 0.71 nm, and the fundamental mordenite unit in the hydrated state typically has a chemical composition of Na8.[(AlO2)8.(SiO2)40].24H2O with larger-diameter 0.7 nm pores.
The initial cation coming from the synthesis may be exchanged totally or partially with alkali metal cations, alkaline earth metal cations, metal cations, ammonium or protons.
The olefins to be used in the process according to the invention may be chosen from a wide range. They contain at least one nonaromatic carbon-carbon double bond. They may generally be represented by the formula: 
in which each of the symbols for R1, R2, R3 and R4, which are identical or different, represents a hydrogen atom, an aryl radical or an alkyl radical, linear, branched or cyclic, which contains from 1 to 20 carbon atoms and may contain one or more unsaturations and/or aromatic groups and/or OR5, SR5, NR5R6, CN, COR5, COOR5, CONR5R6, SiR5R6R7, Si(OR5)R6R7, Si(OR5)(OR6)R7, Si(OR5)(OR6)OR7, SO2R5, SO3R5, POR5R6, OP(O)(OR5)(OR6), NO2 or halogen groups, each of the symbols for R5, R6 and R7 denoting independently a hydrogen atom or an alkyl, cycloalkyl or aryl radical optionally containing one or more unsaturations.
Two of the symbols for R1, R2, R3 and R4 may also represent an unsubstituted or substituted alkylene group: that is to say that the double carbon-carbon bond may be included in a ring, for example in cyclohexene, cyclopentadiene, dicyclopentadiene, etc. The olefin of the invention may equally be an unsaturated or polyunsaturated fatty acid, an ester of an unsaturated or polyunsaturated fatty acid, a derivative of a fatty acid containing at least one double bond, or a mixture of the latter. For example, it may be oleic acid, linoleic acid, linolenic acid, palmitoleic acid, or their esters of natural origin such as triglycerides or of synthetic origin such as, for example, esters of aliphatic alcohols or polyols. These fatty acids and esters may be used alone or mixed such as in natural fats, oils or fats of vegetable or animal origin, and derivatives thereof. Examples are sunflower oil, soybean oil, colza oil, rice bran oil, castor oil, tallow oil, tall oil, and the like. In the frame of the invention, the natural fats or their derivatives may contain some proportion of saturated acids or esters which act like solvents under the operating conditions of the invention.
The olefin of the invention may equally be a terpene, such as pinene, menthene, limonene, etc.
Mixtures of a number of olefins may also be used. By way of example, mention may be made of the mixture of a natural fat with an unfunctionallized aliphatic olefin.
It is preferable to use an olefin such as isobutylene, diisobutylene, triisobutylene, tripropylene, tetrapropylene, a fatty acid, a fatty ester, a mixture of fatty acids or esters, or an oil of vegetable or animal origin possibly mixed with an unfunctionallized aliphatic olefin .
The olefins used according to the invention may also be diluted in solvents. At the end of the reaction these solvents are vented or are separated by distillation. Examples of solvents of this type are saturated aliphatic hydrocarbons, such as methane, ethane, propane, a butane or a pentane. Using mixtures of this type made from olefins and from saturated hydrocarbons can substantially improve the cost-effectiveness of the process of the invention, since starting materials of this type can be less costly than a relatively pure olefin as starting material. For example, instead of pure isobutylene, a cut could be used comprising saturated and unsaturated hydrocarbons containing 4 carbon atoms.
Sulphur may be used in solid form, as a pellet, as a powder or in liquid form. The sulphur/olefin molar ratio may be from 0.4:1 to 2.5:1, and is preferably between 0.5:1 and 2:1.
The H2S/olefin molar ratio may vary over a wide range (from 0.5:1 to 5:1, or even more), but it is preferable to use the least amount of H2S required for satisfactory working of the reaction, or an H2S/olefin ratio of between 0.5:1 and 2:1.
The process according to the invention may be operated batchwise or continuously.
The catalytic efficacy of the zeolite generally becomes apparent from a minimum amount of 0.5% by weight with respect to the amount of olefin. In most cases, the maximum useful amount is of the order of 50% by weight. In a batch process the preferred amount is between 5 and 30%.
In the case of continuous operation of the process, one charge of catalyst may be used for long periods to prepare large amounts of product, and the catalyst/olefin ratio by weight is no longer of great significance.
The process according to the invention may be operated in any appropriate equipment, for example in a reactor equipped with a stirrer, where the catalyst is in suspension in the liquid reaction medium. It may also be operated using a tubular reactor, in which the catalyst is arranged in a fixed bed, in a moving bed or in an expanded bed. It is preferable to use a fixed bed reactor.
The reaction itself may take place within a wide range of temperatures, according with the olefins used and the catalyst employed. It is generally carried out at a temperature of between 20 and 180xc2x0 C., preferably between 70 and 150xc2x0 C.
The reaction is conducted at a pressure appropriate to the conversion of the olefin. It is advantageously worked at between 1 and 50 bar absolute, preferably between 1 and 20 bar absolute. The pressure may vary during the course of the reaction, particularly as a function of the temperature profile and of the progress of the reaction.
After a phase under pressure in a closed reactor where the olefin is converted, it is advantageous for the reactor head space to be set to atmospheric pressure or subatmospheric pressure in order to remove excess H2S and to complete the conversion of the mercaptan formed. In this latter phase it is possible to introduce an inert gas (such as methane, air or nitrogen) in order to entrain residual volatiles, such as H2S, or residual olefin.
In the case of a batchwise reaction, at the end of the reaction the catalyst may be reclaimed by simple filtration and reused.
If it is desired to reduce the odour of the product, or to stabilize the same or reduce its corrosivity, the sulphurated product may be treated by any method known to the person skilled in the art. Methods of this type are described in patents JP 58-140063, U.S. Pat. No. 5,155,275, U.S. Pat. No. 5,206,439, U.S. Pat. No. 5,218,147, U.S. Pat. No. 5,403,961, U.S. Pat. No. 5,457,234, U.S. Pat. No. 5,530,163, U.S. Pat. No. 5,559,271, U.S. Pat. No. 5,091,112, U.S. Pat. No. 5,174,922, U.S. Pat. No. 5,208,382, U.S. Pat. No. 5,242,613, EP 76376 and EP 933 358, for example.